Cardiac surgery often requires that the heart be stilled during the procedure. An arrested heart allows the surgeon sufficient time and a stable environment on which to operate, a particular necessity for lengthy and invasive procedures such as valve replacement. A number of devices and procedures have been developed to enable a physician to stop the heart long enough for a surgical procedure to be performed, and then restart the heart at the termination of the procedure.
Stopped heart procedures are complex and often cause patient trauma during the procedure and during post-operative recovery. Over the years, the application and effectiveness of stopped heart procedures have increased, meanwhile attempts have been made to limit patient trauma recovery time, and overall expense.
To maintain the flow of oxygenated blood during a stopped heart procedure, the heart and lungs must be bypassed during the time that the heart is stopped. This by pass us achieved using a cardiopulmonary bypass (CPB) apparatus. The essential goals of CPB for heart surgery are to provide life-support functions, a motionless, decompressed heart, and a dry, bloodless field of view for the surgeon. In a basic CPB system, the heart is stopped by the infusion of cardioplegia. Oxygen-poor blood is drained by gravity or suctioned from the patient's venous circulation, and is transported to a pump-oxygenator, commonly known as the heart-lung machine, where the blood is exposed to a gaseous mixture that eliminates carbon dioxide and adds oxygen. The venous drainage process may involve placement of a cannula (or cannulae) into the right side of the heart (typically the right atrium), or directly in the major veins (typically the superior vena cava (SVC) and/or inferior vena cava (IVC) or through peripheral vein access sites. An arterial or aortic perfusion cannula is placed in the aorta or another large peripheral artery, such as the common femoral artery, to return oxygenated blood to the patient.
Cardioplegic arrest and CPB are commonly employed during cardiac surgery for treating coronary artery disease and heart valve disease. In coronary artery disease, a buildup of stenotic plaque in the coronary arteries causes the artery to narrow or become occluded. The interruption of the blood flow to the heart causes myocardial infarction, commonly known as a heart attack. Heart valve disease includes two major categories, namely valvular stenosis, which is an obstruction to forward blood flow through the heart valve, and regurgitation, which is the retrograde leakage of blood through the heart valve. Most commonly, valvular stenosis occurs in the aortic valve while regurgitation is typically a congenital condition affecting the mitral valve.
Typically, after the patient's chest has been opened through either a thoracotomy or a stemotomy, a cannula will be inserted into the patient's aortic arch. The insertion of the arterial (aortic) perfusion cannula is usually performed in the following fashion. After the patient's chest has been opened and the pericardium (the protective sac around the heart) has been entered, two concentric purse string sutures are placed into the anterior wall of the ascending aorta just proximal to upstream side of the brachiocephalic trunk. A "choker" tube or sleeve is positioned over the trailing ends of the suture threads to act as a tourniquet for tightening the purse string suture. A small incision is then made through the wall of the aorta in the center of the purse-string sutures. The aortic perfusion cannula is then quickly inserted through that incision into the aorta, taking care to minimize the escape of blood from the puncture site. The purse string sutures are then tightened by means of their respective tourniquets to seal the aortic wall around the perfusion cannula in order to prevent the escape of blood from the aorta. Air is then purged by arterial pressure from the perfusion cannula which is in fluid communication with the pump-oxygenator. A cross-clamp is placed on the aorta just downstream of the aortic root and upstream of the cannula to ensure that no blood flows back toward the aortic valve during CPB.
After CPB has been established, cardioplegia is administered by delivering a cardioplegic solution, such as potassium, magnesium, procaine, or a hypocalcemic solution, to the myocardium by one or a combination of two general techniques, antegrade and retrograde perfusion. Antegrade perfusion of cardioplegia involves the infusion of fluid through the coronary arteries in the normal direction of blood flow. A cannula is typically inserted into the aorta upstream of the aortic clamp and the solution is injected into the aortic root and delivered under pressure in the normal direction of blood flow into the coronary ostia and from there to the myocardium. For procedures on the aortic valve, cardioplegia is typically administered via a transverse aortotomy whereby direct access to the coronary ostia is possible. The cardioplegia is delivered using a wand inserted intermittently into the ostia during the procedure. Retrograde perfusion is accomplished by inserting an occlusion into the coronary sinus and administering cardioplegia upstream of the occlusion and forcing the fluid against the normal flow of the blood into the coronary veins to the myocardial capillary beds.
Once the beating of the heart has been arrested, the surgeon will perform the necessary coronary procedures and repairs. When these repairs have been completed, the arterial and venous cannula will be removed from the surgical area and the entrance sutures tightened to seal the vessel punctures.
The placement of the occluder in the ascending aorta is a particularly delicate operation as the operator must take care so as to not block the left subclavian artery, the brachiocephalic artery, or the left carotid artery, but must instead occlude the aorta just upstream of these aortic branches. Even if the placement of the occluder is proper at the initiation of the coronary repair procedure, the position of the device should be monitored closely to avoid even slight movement as the procedure continues. Movement of the device may result in partial or total closure of the aortic branches, depriving the upper body and brain of the patient of blood during the procedure. Similarly, movement toward the aortic valve and/or the left ventricle of the patient should be avoided to prevent damaging the valve. It would thus be desirable to have a system which could allow imaging of the interior of the vessel to determine proper placement of the cannula within the vessel and to enable imaging of the interior of the vessel intermittently during a procedure.
The design of an endovascularly inserted cannulae must take into account the limited space available in the body passageways used for access to the heart and other regions of interest. The use of multiple cannulae increases the number of percutaneous or direct cut-down procedures required for the procedure and increases the risk or infection and other post-operative complications. Multiple insertions also increase the risk of damage to the internal vasculature and increase the complication and time expenditure for the procedure. It would be most desirable to provide a system which would combine a multitude of functions in one device so that the need for multiple or duplicative devices can be avoided.
The device should have a minimal small cross-sectional diameter to reduce the risk of patient trauma. Particularly with patients having advanced heart disease, scaling and calcium deposits are common on the interior of the femoral and iliac artery and the aorta and the use of large diameter cannula increases the risk of dislodging this stenotic plaque, calcium deposits, and other material that has accumulated on the wall of the vessel. The problem is particularly acute when the femoral artery is accessed as the cannula is advanced against the direction of normal blood flow and consequently against the direction of scaling and accumulation of material on the arterial wall. Viability of the femoral artery may also prove to be problematic when using endovascular insertion of a cannula into the aortic arch. Vessels with an insufficient diameter for the introduction of the cannula assembly, either naturally occurring or through vessel stenosis, can prevent the use of such a system unless some alternate means of arterial or venous access to the region of interest is found.
Regardless of the condition of the vessel pathway, endovascular insertion of a cannula around 80 cm in length into a patient's vascular system is complicated and difficult and may be rendered impossible by the bends, branches, or diseased condition of the vessels of the patient. A cannula system that uses alternate access pathways to the heart and other regions of interest would be desirable. Typically, past procedures have used the femoral artery, the femoral vein, and the jugular vein for coronary access because these are the only vessels with sufficient diameter to accommodate a cannula of the appropriate diameter for cardiac repair and other procedures. A device which could access the heart via smaller pathways, such as the right and left subclavian veins or the left subclavian artery, would be desirable because these pathways provide a shorter and less tortuous path to the region of interest. Also, the use of the left subclavian artery, for example, would help prevent severe brain embolism as any dislodged plague from the artery would most likely pass into the subclavian artery or the descending aorta and then into an arm, leg or abdominal viscera of the patient. Ideally, both endovascular and transvascular insertion of the cannula would be possible.
Access via an abdominal aorta incision, a direct aortic arch stick via an endoscopic trocar, a minimally invasive para-sternotomy or mini-sternotomy or thoracotomy, a central access full sternotomy, or an approach through either atrium and through the mitral and aortic valves would are other applications for an improved cannula in addition to the endovascular applications discussed above. Use of alternate pathways thus would limit the risk of embolic material traveling into either carotid and into the brain.
It is therefore highly desirable to have a system which can be used for minimally invasive surgery to isolate the heart and its coronary arteries from the rest of the arterial system. It is also desirable that the system minimizes the risks of embolism and other complications associated with traditional aortic occlusion techniques. The system would preferably allow multiple functions within a single device to limit obstruction of the surgical field and reduce patient trauma and procedure time. The device should also preferably be of a size which would allow use in multiple venous and arterial access sites.